Recently, as the density of board mounting advances, semiconductor products which are to be mounted on a board are requested to be miniaturized and thinned. In order to realize miniaturization and thinning, the TAB mounting technique using a resin tape has been developed. In a development of a thin semiconductor product using a lead frame, a resin molded type semiconductor device of the single-side molding type in which a semiconductor chip is mounted on a lead frame and the mounting face is molded by a sealing resin has been developed.
Hereinafter, a resin molded type semiconductor device of the prior art will be described. FIG. 5 is a section view showing a resin molded type semiconductor device of the prior art.
In the resin molded type semiconductor device of the prior art shown in FIG. 5, a semiconductor chip 3 is mounted on a die pad portion 2 of a lead frame 1, and terminals (not shown) of the semiconductor chip 3 are electrically connected to inner lead portions 4 of the lead frame 1 by thin metal wires 5. In a single face of the lead frame 1, i.e., the face of the lead frame 1 on which the semiconductor chip 3 is mounted, the outer peripheral region of the semiconductor chip 3 is molded by a sealing resin 6.
In a resin molded type semiconductor device produced so as to have a structure such as shown in FIG. 5 is provided with a structure in which an outer lead portion 7 serving as external terminals is arranged on a bottom face of the semiconductor device Since only the face of the lead frame 1 on which the semiconductor chip 3 is mounted is molded by the sealing resin 6 and the rear face of the lead frame 1 is not substantially molded, it is possible to realize a thin resin molded type semiconductor device.
Next, in a method of manufacturing the resin molded type semiconductor device of the prior art shown in FIG. 5, a tapered shape is first formed at tip end portions of the inner lead portions 4 of the lead frame 1 by mechanical or chemical working, and the semiconductor chip 3 is then bonded onto the lead frame 1. Thereafter, the semiconductor chip 3 is electrically connected to the inner lead portions 4 of the lead frame 1 by the thin metal wires 5, and the face of the lead frame 1 for mounting the semiconductor chip 3 is then molded by the sealing resin 6 by means of transfer molding. In order to form external terminals, finally, the outer lead portion 7 of the lead frame 1 which projects from the sealing resin 6 is worked, thereby completing the resin molded type semiconductor device.
In the prior art, in addition to a resin molded type semiconductor device of the structure shown in FIG. 5, also a structure shown in FIG. 6 is employed.
In the resin molded type semiconductor device shown in FIG. 6, an insulative resin tape 8 on which a semiconductor chip 3 is to be mounted is bonded to tip end portions 4a of inner lead portions 4 of a lead frame 1, thereby forming a die pad portion. The device has a structure in which, after the semiconductor chip 3 is mounted on the resin tape 8, terminals of the semiconductor chip 3 are electrically connected to the inner lead portions 4 by thin metal wires 5, and the face of the lead frame 1 for mounting the semiconductor chip 3 is molded by a sealing resin 6. The resin molded type semiconductor device shown in FIG. 6 has the merit that the device can be made thinner than the resin molded type semiconductor device shown in FIG. 5. Specifically, in the resin molded type semiconductor device shown in FIG. 6, the resin tape 8 is bonded to the lower faces of the inner lead portions 4 of the lead frame 1 and the semiconductor chip 3 is mounted on the upper face of the portion. Therefore, the step difference between the upper faces of the inner lead portions 4 and the upper face of the semiconductor chip 3 is reduced. As a result, also the resin thickness of the sealing resin 6 is reduced, and the resulting resin molded type semiconductor device has a reduced thickness. In the resin molded type semiconductor device shown in FIG. 5, since the semiconductor chip 3 is mounted on the die pad portion 2 which is in the same level as the inner lead portions 4, the thickness of the sealing resin 6 cannot be reduced by such a degree that is attained in the resin molded type semiconductor device shown in FIG. 6.
In order to realize thinning, however, a resin molded type semiconductor device of the prior art has a structure in which substantially only the face of a lead frame on which a semiconductor chip is mounted, i.e., the upper face of the lead frame is molded by a sealing resin. Even when a tapered shape is formed in an inner lead portion, therefore, the contact area between the lead frame and the sealing resin is reduced as a whole, thereby producing a problem in that the adhesiveness is impaired and the reliability of a product is lowered. Since such a device has a structure in which substantially only the single face of the lead frame is resin-molded, there are further problems in that the semiconductor chip is adversely affected by stress of the sealing resin, and that package crack occurs in the sealing resin. When the inner lead portions are connected to the semiconductor chip by thin metal wires and single-side molding is performed, there arises a further problem in that, because of stress in the single-side molding structure, a load due to the stress acts on the inner lead portions which are connected by thin metal wires, and the connecting portions are broken, with the result that a connection failure occurs.
Therefore, it is an object of the invention to provide a resin molded type semiconductor device which solves the above-discussed problems of the prior art, in which the adhesiveness between a lead frame and a sealing resin is maintained and stable connection between thin metal wires and inner lead portions are enabled, which has high reliability, and in which thinning is realized, and a method of manufacturing the semiconductor device.